1. Field of the Invention
The present invention relates to a process for storing information units in the nanometer range by changing the shape of a noble-metal surface.
2. Description of the Related Art
The storage of information, in particular image and data signals, currently takes place predominantly using magnetic or optical recording carriers. The information density which can be achieved using these is determined by the smallest information units which can be written and re-read by the process. In conventional magnetic storage media, these units are determined by the size of the magnetic domains (Wei.beta. domains), from a mechanical point of view by the head gap of the read/write heads used and by the distance of the read/write unit from the actual information carrier. In information carriers where the stored information is produced by a change in optical properties, the limit is the wavelength of the light used. The smallest information units here thus cannot be smaller than about half the wavelength of the light. An increase in storage density in optical recording carriers of this type has in the meantime also been achieved through optical near-field microscopy, where the optical read unit is only a few nanometers above the information-carrying surface. The best information densities achieved here at present are in the order of about 20 nm.
A further increase in the information density is only possible by using near-field techniques with a resolution in the subnanometer range. Suitable methods for this purpose are scanning probe techniques, including the scanning tunneling microscope and the atomic force microscope. These methods allow imaging of surfaces on an atomic scale. It has therefore been proposed to produce information storage media having the highest possible density, namely in the range of the individual atoms or molecules. Success in developing these media would result in information densities in the terabyte/cm.sup.2 range.
A number of proposals have been made for storing information in the nanometer range on inorganic or organic surfaces, including M. A. McCord et al., J. Vac. Sci. Technol. B4, (1986), 86-88, R. M. Silver et al., Appl. Phys. Lett. 51 (1987), 247-249 and U. Staufer et al., J. Vac. Sci. Technol. A6 (1988), 537-539. The deposition of individual atoms has also been reported (R. S. Becker et al., Nature 325 (1987), 415-421).
However, all the proposals disclosed hitherto for the provision of maximum-resolution information storage media which also have, in particular, long-term stability and can be produced within an extremely short time are unsatisfactory.